Cartridge for Ammunition

ABSTRACT

A single ply barrier foil is provided between the propellant in the cartridge casing and the pyrotechnic composition in the primer to prevent nitroglycerin migration from the propellant into the pyrotechnic composition. The single ply barrier foil is formed of ethyl cellulose and a plasticizer and has a thickness of 190 um±10 um.

This invention relates to a cartridge. More particularly, this inventionrelates to a cartridge for ammunition. Still more particularly, thisinvention relates to an arrangement for protecting the primercomposition of ammunition from volatile materials in a propellantcharge.

BACKGROUND OF THE INVENTION

Modern smokeless powder used as a propellant in ammunition containsvarious volatile substances and the particular effect they have on thepriming composition will depend on the ingredients of the composition.If the primer is of the potassium chlorate type containing in additionlead sulfocyanide and trinitrotoluene and the propellant charge isdouble base powder containing nitroglycerine, the primer will graduallybecome desensitized by the nitroglycerine vapor. In fact, the certainvolatiles from the propellant powders will act deleteriously on certainpriming compositions.

As is known, ammunition cartridges are manufactured with a casing; adouble-base propellant having nitroglycerin in the casing and a primerdisposed at one end of the casing and including a pyrotechniccomposition.

It is also known that the potential for nitroglycerin migration from thecartridge casing propellant into the pyrotechnic material in the primermay affect the sensitivity of the pyrotechnic primer material. Theresult of increased or decreased sensitivity of the pyrotechnic materialcreates an uncertain ignition of the cartridge propellant. Thisuncertainly must be avoided to maintain safety to all persons.

In the past, use has been made of a membrane between the primer and thecartridge propellant to block the migration of nitroglycerin into theprimer. For example, U.S. Pat. Nos. 2,340,284, 2,974,592, 3,062,146, and4,386,567 describe the use of a membrane material made from regeneratedcellulose strip in a four ply laminated structure. See also, theNational Military Establishment Specification JAN-C-677 dated 30 Sep.1948 and amended 30 Mar. 1951 and 11 Dec. 1951 for a further example ofthe laminated membrane structure. A nitrocellulose lacquer is applied toboth sides of the regenerated cellulose as the only protection againstnitroglycerin migration from the cartridge double-base propellant intothe pyrotechnic composition in the primer. Any void or lack of completecoverage of the nitrocellulose lacquer coating onto the regeneratedcellulose laminated strip would allow nitroglycerin penetration andvapor migration, as regenerated cellulose, in and by itself, is notnitroglycerin resistant. The volatile constituents of the double-basepropellant in the cartridge can easily transfer into the pyrotechnicprimer composition compromising sensitivity of the ignition.

Multi-ply cellulose regenerated strips are also highly prone todelamination during the end use application and therefore create wasteand loss of productivity.

Regenerated cellulose, also known as Cellophane, is manufactured usingcarbon disulfide, a known toxin and environmentally unfriendly chemical.Carbon disulfide must be recovered and properly disposed of to preventenvironmental concerns. This environmental contamination concernrequires complicated recovery processes or remediation concerns for themanufacturers of cellulose regenerated strip. Many have ceased themanufacturing of this product making availability of the prior artnitrocellulose lacquer coated regenerated cellulose strip difficult ifnot impossible to find.

Accordingly, it is an object of the invention to provide an improvedbarrier for preventing nitroglycerin migration from a cartridgedouble-base propellant into a pyrotechnic composition in a primer.

It is another object of the invention to provide an environmentallyfriendly barrier for preventing nitroglycerin migration from a cartridgedouble-base propellant.

Briefly, the invention is directed to a cartridge comprising a casing, adouble-base propellant disposed in the casing and having nitroglycerintherein and a primer disposed at one end of the casing and including apyrotechnic composition.

In accordance with the invention a single ply barrier foil is disposedbetween the propellant and the pyrotechnic composition to preventnitroglycerin migration from the propellant into the pyrotechniccomposition.

The foil is formed of ethyl cellulose.

Typically, the pyrotechnic composition is of a potassium chlorate typecontaining lead sulfocyanide and trinitrotoluene and the propellant is apowder.

These and other objects and advantages of the invention will become moreapparent from the following detailed description taken in conjunctionwith the accompanying drawings wherein:

FIG. 1 illustrates a side view of a cartridge constructed in accordancewith the invention; and

FIG. 2 illustrates an enlarged cross-sectional view of a primer employedin the cartridge of FIG. 1.

Referring to FIG. 1, the cartridge 1, for example, a 20 millimeter (mm)cartridge, is of conventional construction for ammunition having acasing 2, a double-base propellant 3 disposed in the casing and a primer4 disposed at one end of the casing 2 and including a pyrotechniccomposition 5.

The double-base propellant 3 typically includes nitroglycerin while thepyrotechnic composition 5 is of a potassium chlorate type containinglead sulfocyanide and trinitrotoluene.

In accordance with the invention, a single ply barrier foil 6 isdisposed between the propellant 3 and the pyrotechnic composition 5 toprevent nitroglycerin migration from the propellant 3 into thepyrotechnic composition 5.

As illustrated in FIG. 2, the primer 4 is of conventional structurebeing formed of a cup-shaped casing 7 with an open base that houses anelectrically conductive contact 8 between the pyrotechnic composition 5and the open base of the casing 7. In addition, an insulating liner 9separates the conductive contact 8 from the casing 7. The liner 9 ispreferably formed from polymeric material such as, polypropylenes,polycarbonates, polysulfones, poly(ether imides), poly(amide imides),poly(ether sulfones), poly(benzimide azoles), and poly(ether etherketones).

The pyrotechnic composition 5 is sandwiched between the conductivecontact 8 and the single ply barrier foil 6. An anvil 10 of metal ispress fit into the casing 7 over the top of the foil 6 to secure thefoil 6 in place. As illustrated, the anvil 10 is of cup shape with anopen base to expose the center of the top surface of the foil 6.

The single ply barrier foil 6 is uncoated and is made by cast extrusionor solvent cast process. The foil 6 is of a color, for example, red, inorder to distinguish its presence for ammunition assemblers. In otheruses, the foil 6 is of a light tan to dark tan color and a stack of suchfoils 6 may be sufficiently transparent so that print may be readthrough the stack.

In the solvent cast process, a mixture of ethyl cellulose, plasticizers,solvent(s) and dyes is distributed via a state of the art distributoronto a highly polished belt, such as a stainless steel belt. Thisprocess provides control of the foil thickness to a very tighttolerance. The foil then passes into drying sections to optimize thechemical structure and is finally wound onto cores as a finishedproduct.

By way of example, the ethyl cellulose mixture is made of ethylcellulose powder, medium viscosity Type 70 produced by Dow Chemical ofMidland, Mich. and others; a plasticizer, such as, dibutyl phthylate,diphenyl phosphate, triphenyl phosphate, substituted diphenyl ether,substituted phenols, and alkylated diphenyl oxide; and a solvent, suchas, 80:20 toluene:alcohol, butyl acetate, ethanol, methylene chloride,or ethylene glycol monobutyl ether, alone or in combination.Specifically, substituted diphenyl ether is the preferred plasticizerand methylene chloride is the preferred solvent. The foil 6 has athickness of 190 um±10 um.

The single ply barrier foil 6 does not require a nitrocellulose lacquercoating to prevent nitroglycerin migration. Testing was conducted perthe National Military Establishment Specification JAN-C-677 sectionF-4C. According to the specification, samples approximately 3 inches inlength were suspended horizontally by gripping the ends with a holder.Three drops of nitroglycerin were placed approximately ¾ of the inchapart on each strip at a volume of ±0.06 ml via a class “A” volumetricpipette. The samples were then placed into an oven being held a 50degree Celsius for 48 hours. At the end of that time, the samples wereremoved from the oven, allowed to cool, and the nitroglycerin wasremoved from the strips with blotting paper. The samples were thenremoved from the holder and individually examined for any swelling orsigns that nitroglycerin had passed through the strips.

The clear single ply barrier foil showed that nitroglycerin did not passthrough the barrier.

A single ply barrier foil formulated with a red dye was included in thistest to determine potential influence of the required red color. Resultsof this testing indicate no influence to prevent nitroglycerin migrationresulting from the red color addition.

During the pyrotechnic primer composition 5 loading process, properplacement of an uncoated single ply barrier foil 6 into the primer 4will inhibit migration of the volatile constituent of the cartridgedouble-base propellant 3, nitroglycerin, into the pyrotechniccomposition 5. This foil 6 need not rely on full nitrocellulose lacquercoverage onto both surfaces of a cellulose regenerated strip to preventnitroglycerin intrusion into the pyrotechnic composition 5 in the primer4. The uncoated foil 6 is sufficient, without any surface coatings, towithstand nitroglycerin absorption, migration or vapor permeabilitythrough its structure thus affecting the primer pyrotechnic composition5 detonation timing.

The advantage of using an uncoated single ply barrier foil 6 as amembrane in the ammunition primer 4 is the simplicity of the foil toperform as a nitroglycerin barrier. A single-ply uncoated foil 6 willprevent nitroglycerin migration whereas a 4-ply regenerated cellulosestrip requires a nitrocellulose lacquer coating applied to both sides.Any void in the application of the nitrocellulose lacquer coating willprovide exposed regenerated cellulose strip insufficient, in and byitself, to prevent nitroglycerin migration into the primer pyrotechniccomposition. As a single-ply foil, the foil 6 will not delaminate as thedoes the multi-ply prior art during the end use application process.

Advantageously, the single ply foil 6 is environmentally friendly asopposed to the process to produce lacquer coated regenerated cellulosestrip as described in U.S. Pat. No. 3,983,201 requiring carbon disulfide(CS₂) as part of the manufacturing process. Carbon disulfide (CS₂)requires recovery or costly remediation to protect the environment fromhazard. Acute (short-term) inhalation exposure of humans to carbondisulfide has caused changes in breathing and chest pains. Nausea,vomiting, dizziness, fatigue, headache, mood changes, lethargy, blurredvision, delirium, and convulsions have also been reported in humansacutely exposed by inhalation. Neurologic effects, including behavioraland neurophysiological changes, have been observed in chronic(long-term) human and animal inhalation studies. Reproductive effects,such as decreased sperm count and menstrual disturbances have beenobserved in humans exposed to carbon disulfide by inhalation. Animalstudies support these findings. EPA has not classified carbon disulfidefor human carcinogenicity.

The main sources of information are the Agency for Toxic Substances andDisease Registry's (ATSDR's) Toxicological Profile for Carbon disulfideand EPA's Integrated Risk Information System (IRIS), which containsinformation on oral chronic toxicity and the reference dose (RfD) andinhalation chronic toxicity and the reference concentration (RfC).

The single ply foil 6 is particularly useful as a protective barrierseal in 20 mm medium caliber ammunition preventing the diffusion ofnitroglycerin, an energetic double-base propellant plasticizer, fromcontaminating the pyrotechnic composition 5 in the primer 4. Suchcontamination can lead to premature ignition, delayed ignition, referredto as a “hangfire”, or zero ignition, also known as “misfire”, eachcreating a hazardous situation.

Nitroglycerin Resistance analytical testing of the single ply barrierfoil was conducted in January 2010 and repeated in January 2012 inaccordance with the National Military Establishment SpecificationJAN-C-677, Amendment 2, dated Dec. 11, 1951, Section F-4c. The resultsconcluded that the foil conforms to the requirements of SpecificationJAN-C-677 whereas clear cellulose acetate strips failed.

The single ply barrier foil is manufactured as an environmentallyfriendly product with no limitation of exposure or personal protectiveequipment required. The foil is biologically degradable undercorresponding conditions of decomposition and can be stored on disposalsites without cause of danger.

What is claimed is:
 1. A cartridge comprising a casing; a double-basepropellant disposed in said casing, said propellant having nitroglycerintherein; a primer disposed at one end of said casing and including apyrotechnic composition; and a single ply barrier foil disposed betweensaid propellant and said pyrotechnic composition to preventnitroglycerin migration from said propellant into said pyrotechniccomposition.
 2. A cartridge as set forth in claim 1 wherein saidpyrotechnic composition is of a potassium chlorate type containing leadsulfocyanide and trinitrotoluene and said propellant is a powder.
 3. Acartridge as set forth in claim 1 wherein said single ply barrier foilis formed of cellulose.
 4. A cartridge as set forth in claim 1 whereinsaid single ply barrier foil is formed of ethyl cellulose and aplasticizer.
 5. A cartridge as set forth in claim 1 wherein said singleply barrier has a thickness of 190 um±10 um.
 6. A cartridge as set forthin claim 1 wherein said casing is sized for a 20 millimeter ammunitioncartridge.